1. Field of the Invention
The present invention relates to a process for spraying a one-component coating, sealing or adhesive composition using air-assisted, low pressure spray equipment having an improved spray nozzle.
2. Description of the Prior Art
One-component coating, sealing or adhesive compositions are known and include isocyanate-terminated and alkoxysilane-terminated resins or prepolymers that cure in the presence of atmospheric moisture. Also known are mixtures of isocyanate-terminated resins and blocked co-reactants that are activated in the presence of moisture, such as aldimines, ketimines and oxazolidines. Depending upon the particular application these one-component compositions are often mixed with solvents, pigments or other additives that may not be entirely free of moisture. Any moisture present in these additives can cause premature polymerization of the compositions reducing their storage stability.
It is also known in the prior art to employ processes for reducing the moisture content of the additives prior to blending them with the reactive component. Examples include the addition of moisture scavengers, which are often added in excess amount, based on the moisture present, to ensure complete removal of moisture. However, many of the moisture scavengers also have to removed or neutralized due to their volatility. Due to the steps involved and the amount of time necessary, these existing methods are costly.
While it is possible to mix the reactive components with the additives just prior to use, it is critical that the components are mixed in the right proportions. If the components are mixed in the wrong proportions, then the properties of the resulting products can be substantially affected. Special metering and mixing equipment is often needed to conduct this process on a commercial scale, which is also costly.
Accordingly, it is an object of the present invention to provide a process for mixing the binders for one-component compositions with additives without the need for expensive moisture removal steps. It is an additional object of the present invention to accurately mix the components.
This object may be achieved with the process according to the present invention which utilizes a low pressure, air-assisted spray system to accurately mix the components of the one-component spray according to the present invention. An important feature of the invention is the use of a disposable spray tip and static mixer to accurately mix the binders and additives of the one-component systems. Another important feature of the present invention is the use of an optionally power-assisted caulking gun to deliver the one-component composition to the spray tip.
Copending applications, U.S. Ser. Nos. 09/838,792 and 09/838,794, disclose the use of a disposable spray tip and static mixer in combination with a low pressure, two-component, air-assisted spray system. However, that system is intended for larger applications and does not disclose the use of a caulking gun to deliver the two-component composition. Copending applications, U.S. Ser. Nos. 09/917,309 and 09/917,298, describe the use of a caulking gun to deliver two-component compositions to a static mixer having an optionally removable spray tip. These applications do not disclose mixing the binder for a one-component composition with one or more additives. Copending application, Attorney""s Docket No. MD-01-83A-LS, describes the use of a caulking gun to mix the binder for a one-component composition with one or more additives, but in that application the static mixer is inserted into a shroud.
The present invention relates to a process for spraying a one-component composition by
a) activating the trigger mechanism of a caulking gun having two or more rams and containing two or more cartridges to incrementally advance a ram into operative engagement with each cartridge and dispense a first liquid binder component from a first cartridge and a second liquid additive component from a second cartridge into a static mixer having an optionally removable spray tip,
b) mixing the first component and the second component in the static mixer,
c) discharging the mixed liquid components from the static mixer through the optionally removable spray tip at the downstream end of the static mixer into an atomizing zone,
d) introducing air into the atomizing zone,
e) atomizing the mixed liquid components in the atomizing zone,
f) spraying the atomized liquid components onto a substrate and
g) during an interruption in the spraying process or after termination of the spraying process, discarding the static mixer and the optionally removable spray tip.